fix: mount config directory instead of file for Docker Compose

- Add CONFIG_PATH env support to avoid Docker creating config.json as a directory
- Config Save() now auto-creates parent directories
- Update docker-compose.yml to mount ./config:/app/config
- Update README deployment docs accordingly

cmd/main.go

@@ -15,7 +15,11 @@ import (
 )
 
 func main() {
-	cfg, err := config.Load("config.json")
+	configPath := os.Getenv("CONFIG_PATH")
+	if configPath == "" {
+		configPath = "config.json"
+	}
+	cfg, err := config.Load(configPath)
 	if err != nil {
 		log.Fatalf("Failed to load config: %v", err)
 	}